1. Field of the Invention
The present invention relates to an airbag system designed to protect an occupant of a vehicle during a collision. More specifically, this invention relates to a system and method for protecting an occupant of a vehicle using an overhead airbag system.
2. Description of Related Art
Inflatable airbags are well accepted for use in motor vehicles and have been credited with preventing numerous deaths and injuries. Some statistics estimate that frontal airbags reduce the fatalities in head-on collisions by 25% among drivers using seat belts and by more than 30% among unbelted drivers. Statistics further suggest that with a combination of a seat belt and an airbag, serious chest injuries in frontal collisions can be reduced by 65% and serious head injuries by up to 75%. Airbag use presents clear benefits and vehicle owners are frequently willing to pay the added expense for airbags. In addition, the inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles.
Airbag systems typically include three principal components: an electronic control unit (ECU), an inflator, and an inflatable cushion. The ECU monitors the acceleration and deceleration of the vehicle and determines when accident conditions exist. The ECU is in communication with the inflator and transmits a signal to the inflator when the ECU determines that the vehicle has been involved in an accident.
In response to receipt of the signal, the inflator generates inflation gas. The inflator can be designed to produce inflation gas using various methods. For instance, the inflator may use pyrotechnic techniques or simply release compressed gas. In addition, the inflator may use a combination of both pyrotechnics and compressed gas to produce pressurized inflation gas. The inflation gas, in certain embodiments, includes foam. The inflator in is fluid communication with the inflatable cushion.
The inflatable cushion receives the gas generated by the inflator and rapidly expands as the gas fills the cushion. The inflatable cushion is made from a flexible material, such as fabric. When expanded, the cushion receives the energy of an occupant impact and dissipates the energy such that injuries are minimized or completely avoided.
The positioning of the inflated cushion during a crash is critical to proper protection of an occupant. The inflated cushion should be positioned to shield the occupant from impacting hard surfaces within the vehicle, such as the steering wheel, windshield, or dashboard.
The most common type of airbag system stores the cushion and inflator in a compartment in the steering wheel. This type of airbag system is frequently referred to as a driver's side airbag system. When the vehicle is involved in an accident, the ECU, which is generally not situated in the steering wheel, sends a signal to the inflator. The cushion receives the gas generated by the inflator, expands, and is propelled out of the compartment in the steering wheel. The cushion is fully inflated in a fraction of a second. The inflated cushion prevents the driver from striking the steering wheel and dissipates the kinetic energy of the occupant to minimize injury to the occupant. Similar airbag systems are frequently installed in the passenger side of the dashboard. Unfortunately, these types of airbag systems have several disadvantages including poor protection for out-of-position (OOP) occupants and unaesthetic tear seams on the instrument panel or steering wheel.
Overhead airbags systems have been produced in an attempt to provide better protection for out-of-position vehicle occupants and to avoid the necessity of installing airbags in the steering wheel or dashboard of the vehicle. These airbag systems are stored in a compartment in the roof of a vehicle. When accident conditions exist, the cushion deploys down and away from the roof to a position in front of a protected occupant. The cushion prevents the occupant from striking the dashboard or windshield of the vehicle.
Overhead airbag systems may be designed in a variety of different ways. One type of conventional overhead airbag system includes a fill tube that is sewn along the outside, bottom edge of the cushion. The fill tube is in fluid communication with an inflator. Openings in the fill tube and cushion are aligned to allow the inflation gas to move from the fill tube into the cushion.
Unfortunately, this type of airbag system presents a number of disadvantages. First, it is labor intensive, time-consuming, and costly to sew large portions of the fill tube to the cushion. Also, the fill tube, which carries highly pressurized gas, places significant stress on the cushion during inflation. As a result, additional expense must be incurred to reinforce the area of the cushion to which the tube is sewn, or a stronger material must be used to make the cushion. In either case, the cost of manufacturing and assembly are once again increased. Furthermore, cushion stability can become an issue if the part of the fill tube that runs along the bottom of the cushion contacts an occupant's legs during inflation.
Furthermore, it is desirable to permit the cushion to retain inflation gas during inflation of the cushion, but to vent inflation gas in a controlled manner when the occupant impacts the cushion so that the cushion can better absorb the energy of the impact. Unfortunately, many systems for venting the inflation gas increase the cost of manufacturing the airbag system.
As a consequence, it would be an advancement in the art to provide an overhead airbag system that is more cost-effective and simple to manufacture and assemble than conventional airbag systems. It would be a further advancement in the art to provide an airbag system that retains the fill tube in an elevated position during deployment to prevent occupant contact with the fill tube. It would also be advantageous to permit controlled venting of the inflatable cushion during occupant impact in order to better absorb the energy of the impact.